Water use and nitrogen application for irrigation management of pasture production

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The overall objective of this study was to promote efficient irrigation management of grass pastures (emphasis on ryegrass and kikuyu) by synthesizing available knowledge and generating new knowledge for improving water use efficiency by pastures. Italian ryegrass (Lolium multiflorum) was planted in an experiment conducted at the KwaZulu-Natal Department of Agriculture at Cedara located in the midlands of the KwaZulu-Natal mistbelt, one of the main milk producing areas of South Africa. Another experiment with various treatments was also conducted under a rain shelter at the Hatfield Experimental Farm of the University of Pretoria. It was concluded that at the expense of dry matter production, the highest WUE was achieved under water limiting conditions. Based on the data from this experiment, by irrigating once a week and fertilising with high N application rate after each harvest, optimum yield can be achieved with better quality pasture and a better WUE. The data were used to calibrate the models used in this project. The Soil Water Balance (SWB) model was evaluated at the two sites for different irrigation treatments in two ryegrass growing seasons. The applicability of a remote sensing tool (SEBAL) was shown to predict evapotranspiration at a spatial resolution (30 m) suitable for irrigation scheduling of kikuyu.